This invention relates generally to medical devices and procedures for using such devices and, more particularly, to devices which are introduced into a vessel, cavity, or duct in a human or veterinary patient.
Catheters have long been used in a wide variety of medical procedures for establishing, reestablishing or maintaining passages, cavities, or lumens in vessels, organs or ducts in human and veterinary patients. Such vessels and the like include those of the vascular system, the biliary tract (including the common bile and other ducts) and the urinary tract (including the kidney, the bladder, the ureters and the urethra), as well as the esophagus, the trachea, the intestines, the colon, the rectum, the sinus tract, the fallopian tubes, the cervix and the vagina, among others. All of these may be subject to stricture or narrowing which requires dilation. For example, blood vessels can be blocked or narrowed by arteriosclerosis (atherosclerosis), while esophageal strictures can arise from individual anatomical differences, or from diseases such as connective tissue disorder or cancer.
Catheters useful for dilating or enlarging regions in such vessels and the like often include a nondistending, inflatable balloon which can be positioned across a particular stricture or narrowed region. For example, in percutaneous transluminal angioplasty (PTA), a catheter bearing a collapsed balloon is introduced into a patient""s blood vessel and advanced until the balloon lies across a site to be dilated. The balloon of the catheter is then inflated with a fluid so as to widen the vessel or the like, without trauma to the vessel at the site of treatment.
It is sometimes necessary or desirable to provide the site of dilation with a device or structure which prevents subsequent stenosis (closure) of the site. Stents are a known class of surgical devices which are useful for maintaining open lumens. For example, U.S. Pat. No. 4,580,568 (C. Gianturco, Apr. 8, 1986), U.S. Pat. No. 4,739,762 (J.C. Palmaz, Apr. 26, 1988) and U.S. Pat. No. 4,907,336 (C. Gianturco, Mar. 13, 1990) all disclose stents having a cylindrical shape. Each of these stents is contained by a removable sheath so as to facilitate its introduction into a blood vessel or other body portion. (Stents embodying the invention disclosed in the first of these patents is sold under the name xe2x80x9cZ-stent,xe2x80x9d a trade name of Cook Incorporated.) In the use of each, the sheath is withdrawn after the stent is positioned at the desired site, and only after withdrawal of the sheath is the stent expanded by a balloon catheter (""762 and ""336), or is the stent permitted to self-expand (""568). The expanded stent prevents subsequent stenosis of the site.
In the use of these and other stents, it is highly desirable to minimize the cross-sectional area (profile) of the collapsed stent, as well as that of the retractable sheath and of the catheter on which they are carried. Accordingly, the sheath must typically be made of a thin-walled material which contains the stent in close proximity to the balloon. The combination of these requirements often makes it difficult to retract such a sheath without stretching the sheath or displacing the stent on the balloon. Such a sheath can stretch so much as to fail to uncover the stent, rendering the system for deploying the stent useless. Furthermore, such a sheath can also displace the stent and prevent proper deployment. Moreover, the delivery of a stent to the site of dilation on the same balloon which dilates the site can be subject to other drawbacks. Most notably, friction between the containment sheath and the catheter or stent can make it very difficult to slide the sheath far enough to expose the stent for proper expansion. This drawback can be particularly acute with catheters and stents of small diameter.
U.S. Pat. No. 5,464,419 (H. Glastra, Nov. 7, 1995) discloses a PTA device which appears to lack any sheath at all for containing a stent. Rather, the device includes a spirally wound stent of specific construction which is held in an unexpanded configuration by biologically degradable, thin cords 12. The cords 12 break during expansion of the stent, caused by inflation of a PTA balloon positioned within the spiral stent. The disclosed device can be subject to several drawbacks during use, however. The thin cords 12 are spaced apart, so that the balloon and stent would presumably experience uneven initial expansion in the spaces between the cords. Indeed, the spaced cords pose the potential risk of cutting, breaching or damaging the stent during expansion. Prior to deployment, the spaced cords can give the stent and balloon an irregular degree of stiffness along their length, making the device somewhat more likely to kink during the PTA procedure. Further, the cords can be difficult to affix to the stent, especially to stents of relatively small diameter, such as those intended for deployment in the vascular system.
U.S. Pat. No. 5,316,543 (M. A. Eberbach, May 31, 1994) discloses an apparatus useful in the laparoscopic treatment of hiatal hernias, which includes a rigid outer sleeve having longitudinal recesses and flanges for manual splitting of the sleeve. The patent appears to contain no disclosure or suggestion of the use of such a sleeve for containing a stent prior to deployment of the stent, nor any disclosure or suggestion of any way in which the sleeve could be modified to be used in conjunction with a stent. Moreover, the sleeve is disclosed as being rigid, while the sheaths employed for deploying stents (particularly stents to be positioned in the vascular system) must usually have good flexibility.
It would be highly desirable to have a device or method for deploying a stent which did not require retraction or withdrawal of a containment sheath prior to expansion of the stent. It would also be highly desirable to discover such a device or method which was relatively low cost, which was of relatively straight-forward construction, which possessed high reliability during use, which was easy to remove from the patient if complications arose prior to expansion of the stent, and which did not possess discrete threads which might otherwise damage the stent or catheter during use, or interfere with positioning of the stent.
The foregoing problems are solved and a technical advance is achieved in an illustrative stent deployment device having a catheter and a stent positioned on the catheter. Applicant has discovered that a splittable sleeve which is carried on the catheter, and which includes a portion extending over, more preferably fully over, and containing the stent, can successfully maintain the stent in a collapsed condition during its deployment at a desired location within a vessel or the like by the catheter, without requiring prior withdrawal or retraction of the sleeve. More particularly, Applicants have discovered that expansion of the collapsed stent can be performed by actuation of a mechanism for splitting at least the portion of the sleeve extending over the stent.
In regard to the present invention, xe2x80x9cstentxe2x80x9d is intended to have a broad meaning, and to include not only conventional stents, but also implants, prostheses and other devices which can be positioned within a human or veterinary patient by a catheter. xe2x80x9cSleevexe2x80x9d similarly is intended to have a broad meaning, and to include sheaths, tubes and catheters, as well as sleeves. xe2x80x9cSplitxe2x80x9d is intended to include any way in which the sleeve is severed so as to permit expansion of the stent and removal of the sleeve from the patient, and therefore encompasses splitting, tearing, ripping, fracturing, breaking, bursting, separating and fissuring of the sleeve. Lastly, xe2x80x9cfullyxe2x80x9d is intended to mean merely that the portion of the sleeve extending over the stent completely encircles the stent and covers at least a substantial portion of the stent (preferably, at least the majority of the stent) in a longitudinal direction.
Splitting of the portion of the sleeve over the stent advantageously obviates the frictional resistance to withdrawal of the sleeve that would otherwise result from containment of the sleeve portion upon the stent. The substantial coverage of the sleeve by the stent portion provides the device of the present invention with good uniformity of resistance to kinking during use. The stent can be deployed rapidly with the device of the present invention because no time is wasted in attempting to remove the sleeve from the patient before expansion of the stent occurs. Any balloon employed in the present invention is advantageously subjected to relatively uniform force during expansion, obviating any risk of damage to the balloon or stent during expansion. Also, the device is relatively easy to remove in case unexpected complications require interruption of the deployment procedure.
In a first aspect, the present invention is directed to a stent deployment device first comprising a catheter, a stent positioned on the catheter, and a sleeve carried on the catheter, the sleeve having a portion extending fully over and containing the stent. The stent deployment device of the present invention further comprises a mechanism for splitting at least the portion of the sleeve extending over the stent, thereby permitting expansion of the stent. In a preferred embodiment of this aspect, the sleeve-splitting mechanism comprises an inflatable balloon carried on the catheter, and the stent and the portion of the sleeve extending over the stent are positioned over the balloon. Inflation of the balloon splits at least the portion of the sleeve and permits expansion of the stent. The stent can be self-expanding, or can be expanded by the expansion experienced by the balloon itself during inflation.
The sleeve can be shorter in length than the catheter or can be substantially the same length as the catheter. In either case, the sleeve can include an end fixed to the catheter, or the sleeve can be recessed in the catheter, to prevent longitudinal movement of the sleeve along the catheter. Alternatively, the sleeve can be slidable with respect to the catheter after the portion of the sleeve over the stent has been split.
The sleeve is preferably indistensable and can be composed of a medical grade material such as nylon, polytetrafluoroethylene, polyethylene or a polycaprolactam. A lubricious surface can be provided on the sleeve.
The lubricious surface can comprise a layer of a hydrophilic material on the sleeve or can be formed by surface modification of the sleeve.
Without regard to the length of the sleeve itself, the portion of the sleeve over the stent can be severable from the remainder of the sleeve. In such a case, the portion of the sleeve over the stent remains in the vessel after deployment of the stent. It is preferred, but not required, that at least this severed portion of the sleeve is composed of a medical grade, biodegradable material.
Preferably, at least the portion of the sleeve extending over the stent includes a preferentially splittable, longitudinally extending structure. This structure ensures that the sleeve portion will in fact split upon actuation of the splitting mechanism. The preferentially splittable structure can comprise at least one area of reduced radial thickness. Alternatively, the preferentially splittable structure can comprise splittable nylon such as, for example, a plurality of co-extruded nylon strips.
In another preferred embodiment of this first aspect of the present invention, the sleeve includes a proximal end opposite the portion extending over the stent, and the splitting mechanism comprises a means for splitting the entire length of the sleeve between the proximal sleeve end and the portion of the sleeve extending over the stent. The splitting means can comprise a pair of graspable wings on the proximal end of the sleeve. Alternatively, the splitting means can comprise a partial sleeve segment folded back alongside and extending proximally of the stent, whereby withdrawal of the partial sleeve segment splits the sleeve.
In still another preferred embodiment of this first aspect of the present invention, the splitting mechanism comprises a garrote having a proximal end and a distal end, the distal end of the garrote being connected to the sleeve, and the garrote extending between the stent and the sleeve. Withdrawal of the proximal end of the garrote splits at least the portion of the sleeve over the stent, permitting expansion of the stent.
In yet another preferred embodiment of this first aspect of the present invention, the splitting mechanism comprises a string that passes through the sleeve and out the distal end thereof. The string is looped back on the exterior of the sleeve and through a side port or access hole in the vicinity of the proximal end of the stent and into the passage of the sleeve and out the proximal end thereof. Either end of the string is then pulled to split the sleeve or at least that portion over the stent, thereby permitting expansion of the sleeve.
In still yet another preferred embodiment of this first aspect of the present invention, the splitting mechanism comprises a bulbous end on the catheter. Longitudinal movement of the bulbous catheter end with respect to the sleeve splits at least the portion of the sleeve extending over the stent, thereby permitting expansion of the stent. The bulbous end on the catheter can be solid or can be an inflatable balloon.
In a second aspect, the present invention is directed to a device comprising a specific combination of the preferred elements described above. More particularly, the second aspect of the present invention is directed to such a device as broadly described, but in which at least the portion of the sleeve extending over the stent includes the preferentially splittable, longitudinally extending structure as described; in which the mechanism for splitting at least the sleeve portion comprises an inflatable balloon carried on the catheter; in which the stent and the portion of the sleeve extending over the stent are positioned over the balloon; and in which expansion of the balloon during inflation (a) splits at least the portion of the sleeve, and (b) expands the stent.
In a final aspect, the present invention is directed to a device comprising a further combination of specific preferred elements described above. More particularly, the final aspect of the present invention is directed to a device as described with regard to the second aspect of the invention, but in which the sleeve is substantially the same length as the catheter and has a proximal end fixed to the catheter; in which the sleeve is composed of nylon; and in which the preferentially splittable, longitudinally extending structure included in at least the portion of the sleeve extending over the stent comprises at least one area of reduced radial thickness.
Again, the present invention provides a stent deployment device which is highly advantageous over prior devices and methods of stent deployment. Splitting of the sleeve portion over the stent obviates the frictional resistance to withdrawal of the sleeve that would otherwise result from containment of the sleeve upon the stent. The device possesses good uniformity of resistance to kinking during use. The device of the present invention is often capable of deploying a stent rapidly, because no time is wasted in attempting to remove the sleeve from the patient before expansion of the stent occurs The device can be manufactured in a straight-forward manner and at relatively low cost. If a balloon is employed on the catheter, the balloon is advantageously subjected to relatively uniform force during expansion, obviating any risk of damage to the balloon or stent during expansion. Also, since the device is inserted as a single unit, it is relatively easy to remove in case unexpected patient complications require interruption of the deployment procedure.